Gyrodactylus

Gyrodactylus salaris (GS) is the greatest threat to wild salmon in the River Spey, and the UK as a whole. It is a parasitic freshwater fluke which is indigenous to rivers in parts of Russia, Norway and Sweden, where salmon have evolved resistance to it. However, GS has spread to rivers in Norway, Denmark, Germany, France, Spain and Portugal where native salmon have no resistance, resulting in mass mortality of juvenile fish.

In Norway infected rivers lost 98% of their salmon within 5 years. Infected rivers must be poisoned to remove all fish hosts, and barriers erected to stop salmon entering the river to spawn and generate more hosts. GS can survive for 5 to 7 days without a host in damp conditions (e.g. angling clothing, waders, wet reels, lines or landing nets).

Currently the UK is GS-free

The economic and ecological consequences of GS entering the country and the Spey would be catastrophic.

The parasite can be seen under low power magnification, for example, with a good hand lens. Without magnification, heavily infected parr appear greyish, with excess mucus, and possibly concurrent fungal infections. They attach to the host by the attachment organ, or opisthaptor at one end of the body and feed using glands at the other end. Attachment can cause large wounds and feeding can damage the epidermis, allowing secondary infection. G. salaris can build up to very high infection intensity of several thousand parasites on a single salmon parr.
Particular attention should be paid to anglers who have recently come from, or visited, the following ‘red list’ countries:

Norway
Sweden
Russia
Finland
Denmark
France
Germany
Spain
Portugal

You can download the Scottish Executive’s Gs leaflet ‘Home and Dry’ here